1. Field of the Invention
The present invention relates generally to a split rudder control system for an aircraft which reduces the hinge moments opposing full closure of the split rudder control members from small deflection angles.
2. Discussion of the Prior Art
A type of control system for aircraft that has been found to be very effective throughout the flight range includes opposing control members mounted in the upper and lower surfaces of the aircraft wing which provide control forces by upward pivoting movement of the upper control member from its closed or neutral control position and by downward pivoting movement of the lower control member from its closed or neutral control position. The upper and lower surfaces of these control members in their closed positions form portions of the upper and lower surfaces of the wing near the trailing edge, so that the airflow over the wing near the trailing edge is not disturbed.
Such a control system is disclosed in the following U.S. Pat. Nos.: 1,841,804, 1,875,593, 1,916,475, 1,992,158, 2,045,463, and 2,166,292, all to Hall; 1,854,444 to Barnhart; 2,241,335 to Wedberg; 2,279,615 to Bugatti; and 2,412,647 to Northrop. Depending on the relative operation of the left and right hand pairs of such control members on the wings of the aircraft, the split rudders can function as ailerons, elevators, rudders, speedbrakes, and even flaps.
In U.S. Pat. No. 2,412,647 to Northrop et al., such control members are provided primarily for yaw control of a flying wing aircraft. They are disclosed therein as being located on the aft 40% of each wing near the wing tip, and are said to be extendable simultaneously above and below the wing to produce drag.
With the high speeds of modern aircraft, aerodynamic forces generally assist closure of the control members of a split rudder control system. However, large hinge moment forces which oppose return of the control members to the closed position are applied to the opposing control members at small deflection angles from their closed positions. These forces make full closure of the control members to the closed position a design problem, particularly for a lifting wing with positive aft camber and the attendant positive static pressure near the trailing edge of the wing.
The large opening moment forces occur because the high static pressure near the wing trailing edge is communicated into the cavity between the opposing control members, where it acts on the facing surfaces of the opposing control members to produce high opening hinge moments on the upper control member.
While Hall '463 noted above addresses the problem of overcoming the opening hinge moments on the upper split rudders or ailerons at small deflections, the solution provided by that patent is either a fixed trailing edge tab or an external eared tab. Such constructions call for additional materials and accompanying extra weight, and require additional labor to manufacture and assemble the control system. Additionally, such solutions have a detrimental effect on radar signature and therefore would not be suitable for a stealth type of aircraft.
It was with knowledge of the state of the prior art as just discussed that the present invention has been conceived and reduced to practice.